Lye peeling is traditionally used in fruit and vegetable processing industry due to its ability to produce high quality products. However, the process yields large amount of wastewater with high salinity which has a negative impact on the environment (Garcia and Barrett, 2006a, b; Masanet et al., 2007; Schlimme et al., 1984; Wongsa-Ngasri, 2004). The alternative process of steam peeling results in deteriorated product quality factors including appearance, higher loss in firmness, and lower yield compared to the regular lye peeling method (Garcia and Barrett, 2006a). Furthermore, the process of mechanical peeling by knife cutting suffers from reduced final product yield.
Alternative peeling techniques such as enzymatic peeling, flame-peeling, vacuum-peeling, acid-peeling, freeze-peeling, calcium chloride peeling, and peeling with ohmic heating have been studied on different fruits and vegetables (Rouhana and Mannheim, 1994; (Ben-Shalom and Pinto, 1986; Pretel et al., 1997; Toker and Bayndrl, 2003). Other researchers have also studied modified conventional methods, such as high pressure steam peeling with flash cooling, lye-steam peeling, dry-caustic peeling, and freeze-heat peeling (Smith et al., 1980). However, successful commercialization of these methods has been hampered because of high equipment and processing costs or other reasons such as reduced final product quality.
Infrared (IR) radiation is energy in the electromagnetic wave form that can be used for thermal processing of foodstuff (Pan et al., 2008). Our investigations have recently demonstrated the potential of using IR as an alternative and sustainable tomato peeling technology (Li et al., 2009). Tomato peel loosening involves the loss of rigidity and separation of several cell layers between exocarp and mesocarp due to the breakdown of pectin and the formation of cracks on the tomato surface because of the reduced skin strength. During IR peeling, thermal effects are thought to control the release of the skin although the exact mechanism is unknown. This is mechanistically contrary to the traditional lye peeling whereby the lye solution penetrates the skin and dissolves the pectic and hemicellulosic material in the cell walls via diffusion and removes the pectin which results in the weakening of the network of cell wall and causes the release of the skin (Das and Barringer, 2005). The mechanism for steam peeling is similar to lye peeling, but without dissolving related to the lye. Resulting loss of tissue from steam peeling is typically high as is loss of firmness in the final product, making it less desirable than lye peeling. IR peeling is also different from knife cutting which typically removes a relatively thick layer of tissue rather than just the skin of fruits and vegetables. The novel IR peeling method and use of apparatus in this invention result in products with surprisingly good quality, high yields, as well as excellent color, texture and flavor.
Although prior studies have investigated the potential of IR for peeling, none have been successful without the use of some caustic/lye in addition to application of IR. This invention for the first time claims the use of IR alone as a highly effective method for peeling fruits and vegetables. Previous studies on IR dry caustic peeling proposed that since IR does not require a heating medium for the delivery of energy to the product, such as water, that the process be named “dry peeling” (Hart et al., 1970). The application of IR dry-caustic peeling was studied for white potatoes and peaches and the results exhibited significant decreases in peeling loss, usage of caustic lye and generation of wastewater (Sproul et al., 1975). These examples used both IR and caustic and differ from the claimed invention in that the claimed invention for the first time uses only IR for peeling purposes.
Because of the high heat delivery capability and low penetration depth, IR is a very suitable heating method for efficiently loosening the skin and thereby peeling of fruits and vegetables. Uniform rapid heating of the fruits and vegetables during IR treatment was not previously achieved and is necessary to produce good quality end products. This invention solves these and other previously insurmountable challenges related to IR peeling and enables the user for the first time to take advantage of the IR process to efficiently peel fruits and vegetables commercially.